1. Field of the Invention
The present invention relates to a range finder for measuring the three-dimensional position of a subject.
2. Description of the Related Art
Conventional range finders involve, for example, a finder shown in FIG. 9A. This is designed to irradiate a subject with a longitudinally linear light (or slit light), to sweep the light in the transverse direction and to capture the reflected light thereof to thereby measure the three-dimensional position of the entire subject. Description will be given to the operation in more detail using FIG. 9B.
Light from a light source 3 is formed into longitudinally linear slit light by a slit 10. The slit light is swept by a rotating mirror 4 such that the projection direction of the slit light is horizontal to the subject 11. The rotating mirror 4 is rotated at an angular velocity of .omega. by a rotation control unit 5. The reflected light from the subject 11 is received through a lens 1 by a photosensor array 2 wherein photosensors are arranged two-dimensionally. At this time, a time period t from the sweep start time to the time the light reaches the respective photosensors on the photosensor array 2, is measured by a timing measurement unit 6. The projection direction of the slit light .theta.(t)=.omega..multidot.t at a time when the light reaches the respective photosensors can be thus obtained.
Using the principle of the tigonometrical survey as well as the projection direction .theta. and the positions of photosensors, the three-dimensional position of a point P on the subject is measured by a distant calculating unit 7.
Now, the principle of measuring the three-dimensional position of the point P will be described in a more concrete manner.
A dashed line 901 shown in FIG. 9B denotes the reset position of a rotation angle (that is, the reset position is defined as sweep start time.) For the sake of simple description, a case where the point P on the subject 11 is on the space of FIG. 9B will be also described. In this case, the point P, the center of the lens 1 and the dashed line 901 are assumed to be on the same plane.
The angle .theta..sub.2 (or .theta..sub.i)made between the line of sight from a light-receiving unit of a photosensor S.sub.2 (or S.sub.i) among n photosensors S.sub.1, S.sub.2, . . . , S.sub.n shown in FIG. 9B, to the center of the lens 1, and an optical axis 902 is a fixed angle as shown in FIG. 9B. As for this angle, the same thing is true of other photosensors and it is determined for every photosensor in a design phase.
First, as shown in FIG. 9B, the time at which a photosensor S.sub.2 receives a reflected light from the point P is set at t.sub.2. The time t.sub.2 corresponds to a time period for the rotating mirror 4 rotates from the reset position by an angle of .omega.. At time t.sub.2, .theta.(t.sub.2)can be expressed by formula 1 as follows:
[Formula 1] EQU .theta.(t.sub.2)=.omega..multidot.t.sub.2
Other photosensors have the same relationship. It is noted that a distance from the lens 1 to the rotating mirror 4 is known.
By calculating an angle .theta.(t)for every photosensor S.sub.i using the formula 1, it is possible to measure three-dimensional positions of respective points on the subject 11 in relation to the range finder by using the calculated angle .theta.(t), the angle .theta.i and the distance from the lens 1 to the center of the rotating of the mirror 4, based on the principle of the tigonometrical survey.
In case of using the conventional range finder as described above, however, it is required to measure a time at which light reaches the respective photosensors S.sub.i and to provide time measuring means with the photosensors, respectively. Furthermore, to obtain a resolution of an ordinary distance image, it is required to make photosensor strings into integrated circuits (ICs) and to provide peripheries of the photosensors with time measuring circuits, respectively so as to improve resolutions of the photosensors. Thus, quite high integration is needed. Due to this, dedicated ICs have to be fabricated to realize the system, which makes, in turn, the realization of the system disadvantageously difficult.